This invention relates to the packaging of food. In one aspect, this invention relates to the packaging of fresh foods, e.g. retail-cut red meats, while in another aspect, this invention relates to packaging food with a plastic film. In yet another aspect, this invention relates to packaging food with a film structure having at least one film layer comprising a substantially linear ethylene polymer.
In the modern distribution and marketing of food products, a multitude of different packaging materials are used. One principal category of food packaging materials is plastic film. Many different kinds of plastic film exist, both in composition and structure, and some are tailored to specific applications while others are more generic in nature.
Currently, polyvinyl chloride (PVC) film is the predominate plastic film used to wrap retail-cut red meat and similar products, e.g. fresh fish, poultry, vegetables, fruits, etc., due to its many desirable properties and its low cost relative to other plastic films. Representative of these desirable properties are clarity, oxygen transmission, flexibility, toughness, heat sealability, elastic recovery, and processability. However, most PVC films include a plasticizer to obtain the desired flexibility, and a growing concern exists as to the carcinogenic properties of the most commonly used PVC film plasticizer and the tendency of this plasticizer to migrate from the film to the food product. On a more fundamental level, a growing concern also exists regarding the use in food wrapping applications of any plastic film comprising one or more chlorinated polymers. The concern is based on the tendency for chlorinated polymers to yield corrosive acid when thermally degraded or incinerated, as well as concern regarding the general difficulty involved in recycling chlorinated polymers.
In the search for alternatives to PVC film, various monolayer olefin films, particularly polyethylene films, have been considered but none have been found to be without at least one major flaw that has blocked its commercial acceptability. High density polyethylene (HDPE) is much too inelastic to be useful as a commercial wrap, while the various low density polyethylenes, e.g. low density polyethylene (LDPE), linear low density polyethylene (LLDPE), ultra low density polyethylene (ULDPE), etc., do not possess sufficient elastic recovery, and the film retains impressions or dents caused by handling of the packaged goods by potential purchasers while inspecting its contents. This can be detrimental to the sale value of the food product because the wrapped product will quickly lose its pristine appearance which in turn may cause subsequent potential buyers to intentionally avoid a perfectly good product that now has the appearance of one repeatedly rejected by earlier potential purchasers. The use of nontoxic plasticizers, such as corn oil, has not proven totally satisfactory, particularly with respect to their temperature stability.
Various multilayer films have also been considered (e.g. those taught in U.S. Pat. No. 5,112,674 and in EPO 0 243 965,EPO 0 333 508, and EPO 0 404 969), and significant among these are films made by co-extrusion of polyethylene with an ethylene/.alpha.,.beta.-ethylenically unsaturated carbonyl copolymer, such as ethylene vinyl acetate (EVA) or ethylene acrylic acid (EAA). While these films demonstrate an elastic recovery similar to PVC film, EVA and EAA are relatively expensive copolymers. Moreover, ethylene/.alpha.,.beta.-ethylenically unsaturated carbonyl copolymers are relatively difficult to fabricate, have a tendency to impart an offensive taste and/or odor to the food product, and are known to interfere with anti-fogging agents.
In other food wrap applications, other properties may have importance. For example, in the wrapping of primal cuts of meat (i.e., whole or sectioned carcasses of beef, pork, etc.) for long-distance shipping or long-term storage, shrink and oxygen impermeability are important properties. Consequently, these film are often multilayer structures comprising at least one oxygen barrier, e.g. SARAN (trademark of The Dow Chemical Company for a vinyl chloride --vinylidene chloride copolymer), sandwiched between two layers of a material with good shrink and abuse properties, e.g. LLDPE. In the packaging of foods using form-fill-seal technology, hot tack is an important property and, accordingly, multilayer film structures with at least one skin layer comprising LLDPE or ionomer as a hot tack heat seal layer. The other film layers impart the desired properties relative to the food to be packaged, e.g. SARAN for an oxygen barrier, PVC for elastic recovery, etc.